f2fs: fix return value in f2fs_ioc_commit_atomic_write

In f2fs_ioc_commit_atomic_write, if file is volatile, return -EINVAL to
indicate that commit failure.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>